Children as young as six months old will be tested in the study
Scientists are looking for children as young as six months old to try out two new swine flu vaccines.
Five laboratories across the country will be testing 1,000 youngsters - from six months to 12 years of age - to see which vaccine works best.
The study will focus on Southampton, Oxford, London, Bristol and Devon and will monitor their immune reactions, and any fever or muscle soreness.
The vaccines have already been tested in adults - and showed good results.
Vaccinations for high risk groups could be starting as early as next month.
The work is a collaboration between the University of Southampton Wellcome Trust Clinical Research Facility, the University of Oxford, the University of Bristol, St George's Medical School at University of London, the Royal Devon and Exeter NHS Trust and the Health Protection Agency.
The laboratories, led by the Oxford team, hope to start testing the children within two weeks.
The study in Southampton, which will test 250 children, is being led by Dr Saul Faust, senior lecturer in child health at the University of Southampton and honorary consultant at Southampton University Hospitals NHS Trust.
He said: "Children are one of the age groups most vulnerable to swine flu infection, so it is vital that we obtain information on their response to these vaccines.
"This study will help in decisions about which vaccine will be best for protecting children."
Millions of doses of the two swine flu vaccines have been purchased for use across the UK by the Department of Health to "control the expected outbreak this autumn, but information about their use in children is limited", a University of Southampton spokesperson said.